In Robin Hood you must perform many heroic deeds to change the public impression of you from "villain" to "hero." To he ultimate aim is to retake your castle, which is captured in the intro sequence. This involves bringing together your band of merry men, and killing the Sheriff and his guards. There are around 6 extra items you can find in the game, most of which aren't essential but make the game a lot easier. The whole interface is similar to Populous: you don't direct Robin directly but with icons which are placed around the screen.
The AI citizens of Sherwood go about their lives as normal, so it's another game that you can spend just watching and wandering through rather than trying to complete.